The use of double panes of glass and even triple panes of glass in order to provide insulation against the transmission of heat energy as well as noise energy is well-known. Such window constructions typically include two or more spaced apart parallel panes of glass, usually mounted in an elastomeric material such as rubber, for example. Means for compressing the rubber so as to seal the glass panes therein and to prevent air from leaking into and out of the space between the panes is also provided.
It is understood that it is necessary that the dead air space intermediate the panes of glass is effectively sealed. Not only is the insulating value of such windows dependent upon the maintenance of an adequate seal, but in addition, visibility also may depend on maintaining such seal. In the event moisture condenses on the inner surface of the glass, or a film of grease or dirt accumulates thereon, visibility will be adversely affected.
Many attempts have been made from time to time to provide a satisfactory solution to the problem. These attempts have involved the use of rubber sealing strips such as gaskets, with various means for compressing the gaskets against the panes. Experience, however, shows that such constructions do not consistently provide sufficient uniform pressure to provide an effective air-tight seal when subjected to conventional manufacturing techniques, particularly in wooden sash constructions.
The use of a conventional rubber sealing strip in the normal way, that is, without special efforts to achieve uniform compression, substantially reduces circulation between the ambient air and the space between the panes. One result is that the insulating effectiveness may reach a reasonably acceptable level. Another is that the accumulation of dirt between the panes is retarded; however, when it accumulates, the situation is just as unsatisfactory as the case of an ordinary storm window. In the event humid air enters the space between the panes, and the ambient temperature drops, condensation of moisture occurs between the panes and, since circulation between the ambient air in the space between the panes is slow, the window remains "fogged" for various substantial periods of time. Thus, in order to decrease the dirt problem, one finds that the condesation problems are quite detrimental to adequate visibility.
Various forms of factory sealed windows when maintained sealed as by fused metal or glass offer high quality insulation. Where pressure elastomeric gasket seals or flexible adhesive seals are provided, the dirt and condensation problem is minimized. However, such windows are of relatively high expense, involves high insurance costs, and are expensive and difficult to repair and replace. The fact that factory fabricated insulating windows can be purchased only in certain standard sizes also placed limitations in design, especially when curved windows are involved.
The fact that such expensive solutions have nevertheless found very substantial commercial success clearly indicates that the problem itself, that is obtaining good insulating quality without visibility impairment, is a pressing problem and a problem of great commercial importance, and one for which no obvious answer exists.
Thus, there remains a problem of providing a seal as good as presently possible only with factory fabricated insulating windows, which is at the same time inexpensive, readily adapted to any size or shape of window including curved windows, and which can be installed and repaired at the job site rather than requiring factory fabrication.
Air-type seals are well-known in the technicology, but the problem in connection with the insulating windows is to obtain a seal which is not only effective, but also extremely simple in design and installation and low in cost. Complicated constructions make excellent air-type seals for scientific and industrial apparatus, but have no place in construction of residential, commercial, and industrial buildings, or in vehicles such as automobiles, buses, trains, and air craft.
The difficulties which must be overcome in the solution of this problem include the following:
1. Considerable force must be necessary to make a tight seal, but glass panes must not be broken nor stressed so that the glass panes would break upon temperature and atmospheric pressure changes or additional stress.
2. It is not sufficient to provide an excessively large force at some points and inadequate force elsewhere. "Averages" are not what counts here, but rather uniform seal around the peripheral facing edges of the adjacent surfaces of the associated glass panes.
3. Expansions and contractions caused by temperature variations with seasonal variations, or with changes in elevation, for example during shipment, must be accounted for without causing breakage on one hand and/or air leakage on the other.
Heretofore pressure variations between the gas within the space between the facing surfaces of double glazed window construction and the atmosphere as caused by temperature changes or changes in atmospheric pressure have been compensated to reduce the pressure differential across the seals between the adjacent panes by providing an auxilliary chamber containing a fixed amount of gas which is at the pressure within the space and is varied in volume to match or approach atmospheric pressure U.S. Pat. No. 1,852,661 entitled "SHOW CASE REFRIGERATOR" to Larkin discloses syphons exterior of the double glazed window of a show case and in gas flow communication with the space between the panes of glass that expand and contract to compensate for difference in pressure between the interior and exterior of the space. U.S. Pat. No. 2,015,808 entitled "DOUBLE WINDOW CONSTRUCTION" Miller et al. discloses a frame including a cavity containing a tube of thin metal or rubber which may be collapsed and expanded when varying air pressures are applied to the unit. The prior art has also attempted to eliminate the problem of fogging between adjacent panes of glass of a hermatically sealed window or transparent panel which is double glazed by introducing dry gas into the space between the panes and/or by including a desiccant in a container in gas communication with the space. U.S. Pat. No. 1,913,205 entitled "ANTI-FOGGING DEVICE" Lenhart shows a tray of desiccant screened from in gas flow communication with the space between the panes of a double glazed window. Alternatively, a number of patents disclosed valves providing admission of gas to the space between lights of double glazed windows and suggest the temporary connection of sources of dry gas for drying and flushing such space. These U.S. Pat. Nos. include the following: 1,495,948--Carney, 1,851,515-- Hunt et al., 2,009,142--Marsh, 2,117,581--Stoneback, 2,756,467--Etling, 2,880,475--Mills.
Leaks in the units of the prior art having gas drying arrangements have resulted in the admission of sufficient moisture to cause the drying capabilities of the desiccant in those units containing desiccant and ultimate fogging of the interior of the window. These leaks have been attributed to pressure differentials between the interior and exterior. In U.S. Pat. No. 2,083,622 Summers discloses the concept of a pressure equilization mechanism combined with a drying mechanism for a double walled panel which in some embodiments is of transparent materials. The combination of the Summers is cumbersome and does not lend itself to application to conventional window construction. Further, if some leakage of moisture into the system does occur, the desiccant can be exhausted with resultant failure of the system.
A replaceable desiccant supply has been proposed for double glazed windows, such as for example, U.S. Pat. No. 2,088,738 entitled "DOUBLE GLAZED WINDOW" Fox wherein there is disclosed a detachable casing containing a desiccant which is screw coupled in a cavity in the face of the window frame in gas flow communication with the space between the transparent panes so that it can be replaced when the desiccant is spent. However, this casing protrudes from the window frame and offers an unsightly obstruction. Further, it is a dead end to the gas conduit from the window enclosure and with no circulating means and therefore offers only limited access to the gas within the enclosure.
U.S. Pat. No. 3,685,239 entitled "HERMATICALLY SEALED DOUBLE GLAZED WINDOW UNIT AND METHOD OF SEALING SAME" McCurdy et al. discloses a rechargeable desiccant chamber in the wall of a window frame wherein a lower port can be opened to withdraw spent granular desiccant and an upper port through which a new charge of desiccant can be introduced.
In a previously granted U.S. Pat. No. 4,065,894 entitled "REPLACEABLE DOUBLE GLAZED WINDOW DEFOGGING APPLIANCE AND WINDOW STRUCTURE THEREFORE", it was explained that certain of the shortcomings of the prior art could be overcome by utilizing a unitary, atmospheric pressure equalization chamber and drying chamber including a sealed flexible walled container having means providing communication from its interior to the space between a double-glazed window structure. The communication means, although operatively satisfactory, were somewhat complex and required the associated window frame to be particularly configured to accept the communication means which were typically in the form of a hollow tube or duct.